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Cold front in the kitchen
It’s easy to think of our homes as monolithic structures with uniform climatic conditions throughout, but that couldn’t be further from the truth. Different rooms, even different parts of the same room, have their own temperature, humidity and light levels. Your house has its own weather. Temperature differences of 40 °C between the coldest and hottest places in the house are not uncommon, says Richard Corsi at the University of Texas, who has spent two decades studying indoor air quality. Many of the changes to the indoor weather are what you would expect. Switching a radiator on or sunlight shining through a window will increase temperatures. And temperature differences across your home drive indoor airflow. “If the air is really hot
“Parties in your home create their very own meteorological effects” in the basement in the winter and cooler in the occupied space, the warm air is going to move towards the cool air,” says Corsi. But some of the indoor weather patterns are far less obvious – and we are responsible. “All of us are 60 to 100 watt light bulbs, depending on our size,” says Corsi. Our warming of the air around us can take on particular significance when everyone congregates in a room at a party. “Warm air rises from us towards the ceiling and tends to bring in cooler air from elsewhere in the room to replace it. So you have these circulatory patterns of air rising and falling,” says Corsi. The parties in your home don’t just go with a bang, they create their own meteorological phenomena. Just as the planet has extreme weather, so do our homes. The most extreme conditions are in places we don’t see, such as the attic and the spaces within our walls. “If a house has air conditioning, then the coldest place in the summer will be about 12 °C in the air that’s flying from the supply duct,” says Corsi. “In the occupied spaces it might be 23 °C, and external wall cavities and attics can get up to 50 °C.” It doesn’t just get hot. When the sun beats on an external wall, it raises the pressure in the cavity between outside and inside. Walls aren’t just walls, they are frontal systems too! 36 | NewScientist | 7 February 2015
berndnaut Smilde,nimbus,2010,digital c-type print 75x112cm. courtesy of the artist and ronchini gallery,london,uk
Cold front in the kitchen
And now the weather... Temperature differences across a home can be extreme
18°C
50°C 13°C 23°C 35°C 18-32°C source: richard corsi
This is your life We spend a surprising amount of time inside
78.7 years – average life expectancy
70
years spent inside buildings
50
years spent in residential buildings
26
years spent lying on a mattress
2bn
the number of buildings thought to exist in the world, although no one knows for sure
$20tn
the value of residential building stock in the US – making it the country’s number one asset
Indoor chemistry Every moment of every day, chemical reactions are taking place in the air and on almost every surface of our homes. The primary driver of this indoor chemistry is ozone, a highly reactive molecule made up of three oxygen atoms. Most of it comes into our homes from outside, although relatively small amounts come from air purifiers, laser printers and heating, ventilation and air conditioning (HVAC) systems. It doesn’t hang around for long. “Indoor ozone tends to be much lower concentration than outdoor ozone, but that’s because it reacts with so many things indoors,” says Richard Corsi at the University of Texas. “So there’s a lot of interest in ozone reaction products.” Ozone reacts with anything scented, such as air fresheners and cleaners. “All of those scented compounds have carbon-carbon double bonds and ozone loves to attack those things,” says Corsi. The proliferation of fragrances in our homes means that, in some cases, the chemistry is unknown. “We are using so many scents indoors these days and when they oxidise they form things we just don’t find outdoors,” says Corsi. “No one has done the toxicology on them.” He says we should be paying attention to peroxides and dicarbonyls because they have a similar structure to other chemicals known to be toxic or cause severe irritations. “There are red flags flying all over the place,” he says. Ozone attacks the carbon-carbon double bonds elsewhere too – in the styrene in our carpets, in our soaps and even in the oils on our skin. It leads to the formation of carbonyls, including formaldehyde, the pungent gas used as a preservative in mortuaries. “In high enough levels it can cause upper respiratory problems and eye irritation, that kind of thing,” says Corsi. Other short-lived molecules called Criegee biradicals are also produced by ozone chemistry. These are extremely reactive and lead to the formation of a wide range of by-products, including some that are irritants or toxic. A move towards greener living doesn’t help. Many “natural” cleaning products contain terpenes or terpenoids, organic molecules found in plants that are highly reactive with ozone. “Tighter, more draft-resistant homes and more green products have led to our homes becoming intense chemical reactors,” says Corsi.
Not so fresh air
Three unexpected pollutants Dishwashers:
Dishwasher detergent can contain sodium hypochlorite and when it reacts with some foods, particularly meat and tomatoes, the result is chloroform. Scented candles:
The slow-burning scenting agents only have a millisecond to burn in the flame and often don’t burn completely. Many lead to the formation of ultrafine particles that can find their way into our lungs. Vacuum cleaners:
The wheels flick up particles that contain allergens and pollutants into the air.
Many indoor pollutants are released into our homes by the things we bring into them. Formaldehyde, for example, comes from the likes of plywood and cosmetics. There’s also the release of semi-volatile organic compounds, such as the flame retardants used in furniture and bed mattresses. However, certain materials soak up what’s been released and the products of indoor chemistry. “The polyurethane foam that’s often used in furniture and as foam padding beneath carpet is a tremendous sink for pollutants,” says Corsi. As is the gypsum plasterboard that lines many of our walls. The weather inside our homes (see “Cold front in the kitchen”, left) has a big impact on pollution levels. The high temperatures sometimes found in the spaces between walls speed up the rate of chemical reactions. “As a really rough rule, if you increase the temperature of a material by 10 °C, you are going to double the emission rates from it,” Corsi says. And when the temperature rises, so does the pressure in the spaces – pushing the dirty air into our rooms. “Electrical outlets and cracks in the walls are really leaky,” says Corsi. > 7 February 2015 | NewScientist | 37
“Parties in your home create their very own meteorological effects” in the basement in the winter and cooler in the occupied space, the warm air is going to move towards the cool air,” says Corsi. But some of the indoor weather patterns are far less obvious – and we are responsible. “All of us are 60 to 100 watt light bulbs, depending on our size,” says Corsi. Our warming of the air around us can take on particular significance when everyone congregates in a room at a party. “Warm air rises from us towards the ceiling and tends to bring in cooler air from elsewhere in the room to replace it. So you have these circulatory patterns of air rising and falling,” says Corsi. The parties in your home don’t just go with a bang, they create their own meteorological phenomena. Just as the planet has extreme weather, so do our homes. The most extreme conditions are in places we don’t see, such as the attic and the spaces within our walls. “If a house has air conditioning, then the coldest place in the summer will be about 12 °C in the air that’s flying from the supply duct,” says Corsi. “In the occupied spaces it might be 23 °C, and external wall cavities and attics can get up to 50 °C.” It doesn’t just get hot. When the sun beats on an external wall, it raises the pressure in the cavity between outside and inside. Walls aren’t just walls, they are frontal systems too! 36 | NewScientist | 7 February 2015
berndnaut Smilde,nimbus,2010,digital c-type print 75x112cm. courtesy of the artist and ronchini gallery,london,uk
Cold front in the kitchen
And now the weather... Temperature differences across a home can be extreme
18°C
50°C 13°C 23°C 35°C 18-32°C source: richard corsi
This is your life We spend a surprising amount of time inside
78.7 years – average life expectancy
70
years spent inside buildings
50
years spent in residential buildings
26
years spent lying on a mattress
2bn
the number of buildings thought to exist in the world, although no one knows for sure
$20tn
the value of residential building stock in the US – making it the country’s number one asset
Indoor chemistry Every moment of every day, chemical reactions are taking place in the air and on almost every surface of our homes. The primary driver of this indoor chemistry is ozone, a highly reactive molecule made up of three oxygen atoms. Most of it comes into our homes from outside, although relatively small amounts come from air purifiers, laser printers and heating, ventilation and air conditioning (HVAC) systems. It doesn’t hang around for long. “Indoor ozone tends to be much lower concentration than outdoor ozone, but that’s because it reacts with so many things indoors,” says Richard Corsi at the University of Texas. “So there’s a lot of interest in ozone reaction products.” Ozone reacts with anything scented, such as air fresheners and cleaners. “All of those scented compounds have carbon-carbon double bonds and ozone loves to attack those things,” says Corsi. The proliferation of fragrances in our homes means that, in some cases, the chemistry is unknown. “We are using so many scents indoors these days and when they oxidise they form things we just don’t find outdoors,” says Corsi. “No one has done the toxicology on them.” He says we should be paying attention to peroxides and dicarbonyls because they have a similar structure to other chemicals known to be toxic or cause severe irritations. “There are red flags flying all over the place,” he says. Ozone attacks the carbon-carbon double bonds elsewhere too – in the styrene in our carpets, in our soaps and even in the oils on our skin. It leads to the formation of carbonyls, including formaldehyde, the pungent gas used as a preservative in mortuaries. “In high enough levels it can cause upper respiratory problems and eye irritation, that kind of thing,” says Corsi. Other short-lived molecules called Criegee biradicals are also produced by ozone chemistry. These are extremely reactive and lead to the formation of a wide range of by-products, including some that are irritants or toxic. A move towards greener living doesn’t help. Many “natural” cleaning products contain terpenes or terpenoids, organic molecules found in plants that are highly reactive with ozone. “Tighter, more draft-resistant homes and more green products have led to our homes becoming intense chemical reactors,” says Corsi.
Not so fresh air
Three unexpected pollutants Dishwashers:
Dishwasher detergent can contain sodium hypochlorite and when it reacts with some foods, particularly meat and tomatoes, the result is chloroform. Scented candles:
The slow-burning scenting agents only have a millisecond to burn in the flame and often don’t burn completely. Many lead to the formation of ultrafine particles that can find their way into our lungs. Vacuum cleaners:
The wheels flick up particles that contain allergens and pollutants into the air.
Many indoor pollutants are released into our homes by the things we bring into them. Formaldehyde, for example, comes from the likes of plywood and cosmetics. There’s also the release of semi-volatile organic compounds, such as the flame retardants used in furniture and bed mattresses. However, certain materials soak up what’s been released and the products of indoor chemistry. “The polyurethane foam that’s often used in furniture and as foam padding beneath carpet is a tremendous sink for pollutants,” says Corsi. As is the gypsum plasterboard that lines many of our walls. The weather inside our homes (see “Cold front in the kitchen”, left) has a big impact on pollution levels. The high temperatures sometimes found in the spaces between walls speed up the rate of chemical reactions. “As a really rough rule, if you increase the temperature of a material by 10 °C, you are going to double the emission rates from it,” Corsi says. And when the temperature rises, so does the pressure in the spaces – pushing the dirty air into our rooms. “Electrical outlets and cracks in the walls are really leaky,” says Corsi. > 7 February 2015 | NewScientist | 37